The present invention relates to a clip for spacing ducts one from the other and to a duct assembly including the spacer clip. More particularly, the present invention relates to a clip disposable between a pair of inner and outer tubes or ducts for spacing and maintaining substantial concentricity of the tubes one with respect to the other and to the tube assembly utilizing such spacer clips.
In the design of ducts utilized for flowing fluids, for example concentric ducts utilized in aircraft for flowing air at different temperatures, there are often stringent requirements. Such requirements include avoidance of heat transfer from one duct to the other or to its surrounding support and ancillary parts and accommodation for thermal expansion and/or twisting of the ducts or tubes relative to one another. Further, in concentric ducts or tubes of this type wherein fluid at one temperature flows through an inner tube and fluid at a higher or lower temperature flows through the annular space between the inner and outer tubes, the support structure for the inner tube must not substantially impede the flow of fluid through the annular space between the tubes. Thus, it is important, in addition to the foregoing requirements, that any clip designed to space the concentric tubes one from the other present a minimum frontal area to the fluid flowing in the annular space between the tubes. Still further, in the aircraft environment, it is desirable to minimize the weight of the spacers or clips used to space the ducts or tubes one from the other.
Many designs for flowing fluid at different temperatures through concentric or near concentric fluid passages have been proposed and constructed in the past. U.S. Pat. Nos. 4,033,381, 3,782,452, 4,014,369, 2,962,053, 3,126,918, and 2,875,987 are representative of such proposals and constructions. However, each of these fails to meet one or more of the above-noted requirements, e.g., permits substantial heat transfer between the concentric ducts, cannot accommodate expansion or contraction of the ducts relative to one another, or impedes the flow of air through the space between the inner and outer tubes by reason of the support structures necessary to interconnect and space the tubes.